Axial alignment assembly, and charged particle microscope comprising such alignment assembly

Abstract

To provide an axial alignment assembly that can achieve required tolerances.SOLUTION: An axial alignment assembly 100 comprises: a first body 1101 comprising a cylindrical outer jacket and having a first alignment axis; and a second body 201 comprising a cylindrical inner jacket and having a second alignment axis, where the second body is positioned relative to the first body such that the inner jacket faces the outer jacket and such that an annular recess is formed between the inner jacket and the outer jacket. The axial alignment assembly further comprises a plurality of resilient elements 301 that are positioned within the annular recess, where each resilient element is in contact with the outer jacket of the first body and with the inner jacket of the second body and exerts a force on the outer jacket and on the inner jacket for aligning the first alignment axis and the second alignment axis.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] Summary The present invention relates to an axial alignment assembly comprising a first body having a first axial alignment axis and a second body having a second axial alignment axis, the axial alignment assembly being arranged to substantially align the first and second axial alignment axes with each other.

[0002] The present invention also relates to a charged particle microscope comprising such an axial alignment assembly.

[0003] Charged particle microscopes are well known and are increasing in importance as a technique for imaging microscopic objects, particularly in the form of electron microscopes. Historically, the basic types of electron microscopes have evolved into various well-known device types such as Transmission Electron Microscopes (TEMs), Scanning Electron Microscopes (SEMs), Scanning Transmission Electron Microscopes (STEMs), etc., and also into various sub-types such as so-called "dual beam" devices (e.g., FIB-SEM) that enable support such as ion beam milling or ion beam induced deposition (IBID), and that employ a further "machining" focused ion beam (FIB). A person skilled in the art will be familiar with the various different types of charged particle microscopes. A person skilled in the art will be proficient in different charged particle microscopy methods.

[0004] In an SEM, when a scanning electron beam irradiates a sample, "secondary" radiation is emitted from the sample in the form of secondary electrons, backscattered electrons, X-rays and cathodoluminescence (infrared, visible and / or ultraviolet photons). One or more components of this emitted radiation can be detected and used for sample analysis.

[0005] In TEM (Telescope-Emission Microscopy), an electron beam is passed through a sample, and an image is formed from the interaction between the sample and the electrons as the beam passes through the sample. This image is then magnified and focused on an imaging device, such as a fluorescent screen, a layer of photographic film, or a sensor such as a scintillator attached to a charge-coupled device (CCD). The scintillator converts primary electrons in the microscope into photons, which the CCD can then detect.

[0006] A charged particle microscope comprises several modules that must be precisely aligned with a common axial alignment axis. This common axial alignment axis is often the electron-optical axis. Modules requiring precise alignment include optical modules such as electromagnetic lenses, particularly the pole pieces of these electromagnetic lenses. For example, the tolerance required for the alignment of the upper and lower pole pieces can be as small as 1 μm. These tight tolerances are sometimes required in other mechanical systems as well.

[0007] The object of this disclosure is to provide an axial alignment assembly that provides these required tolerances or at least improves upon existing axial alignment assemblies. In particular, the object is to provide an improved charged particle microscope by incorporating such an axial alignment assembly.

[0008] For this purpose, an axial alignment assembly as defined in claim 1 is provided.

[0009] As defined herein, an axial alignment assembly comprises a first body having a substantially cylindrical outer jacket. The first body comprises a first alignment axis, which generally corresponds to the longitudinal axis of the cylinder defined by the cylindrical outer jacket. The first body may be, for example, an optical module of a charged particle microscope, such as a pole piece of an electromagnetic lens. The first body may comprise a hollow bore centered with respect to the first alignment axis. Other embodiments of the first body are also, of course, conceivable.

[0010] As defined herein, an axial alignment assembly comprises a second body having a substantially cylindrical inner jacket. The second body comprises a second alignment axis, which substantially corresponds to the longitudinal axis of a (virtual) cylinder defined by the cylindrical inner jacket. The second body is positioned relative to the first body such that the inner jacket of the first body faces the outer jacket of the second body. In other words, at least a portion of the first body is positioned within a cylindrical gap defined by the virtual cylinder. The size and dimensions of the first body and the size and dimensions of the cylindrical gap are such that an annular recess is formed between the inner jacket and the outer jacket. Thus, a substantially annular recess is formed between the inner jacket and the outer jacket. The recess may have a nominal width of at least several tens of millimeters or several tens of micrometers.

[0011] Furthermore, the axial alignment assembly as defined herein also comprises a plurality of elastic elements positioned within the annular recess. These elastic elements may be of virtually any shape, as long as at least one dimension of these elastic elements exceeds the nominal size of the annular recess. In practical embodiments, the elastic elements are substantially spherical, and the diameter of the spherical elastic elements exceeds the nominal size of the annular recess, i.e., the distance between the inner and outer jackets. Each of the plurality of elastic elements as defined herein is in contact with the outer jacket of the first body and the inner jacket of the second body. The elastic elements exert force on the outer and inner jackets, thereby aligning the first alignment axis with the second alignment axis, and thus the first body is aligned with the second body.

[0012] By using an elastic element in the annular recess formed by the outer cylindrical jacket and the inner cylindrical jacket, good centering of the two bodies, i.e., axial alignment, is ensured despite the large dimensional and shape deviations that may occur between the two bodies and the elastic element.

[0013] It is known from applicant name NL10257037C that an axial assembly using plastic balls is provided. In this disclosure, two bodies that need to be aligned are provided with corresponding V-shaped annular grooves. The two bodies are oriented relative to each other such that the two V-shaped annular grooves from a substantially rectangular annular groove have four contact surfaces. By providing plastic balls in the grooves and pushing the two bodies toward each other, for example using a clamping force, the spherical balls make contact with each of the four contact surfaces of the annular grooves, ensuring the axial alignment of the two bodies.

[0014] One of the drawbacks of this known axial alignment assembly is that this V-groove design requires the two bodies to be "pulled together." The alignment assembly can function by fixing the two bodies together and pressing the plastic balls against the four contact surfaces. The clamping force required to deform the balls is considerable. One option to reduce the clamping force is to use "softer" balls, i.e., balls that can be compressed more easily, but this has the negative side effect of reducing the force used to align the two bodies.

[0015] In the axial alignment assembly as defined herein, the outer and inner jackets are used to form an annular recess in which an elastic element is provided. This is advantageous over the alignment assembly described in NL10257037C because the axial alignment assembly according to the present invention does not require the presence of four contact surfaces and does not require the use of axial clamping force. This provides an improved axial alignment assembly that can further provide tolerances of about 1 μm. Thus, the object of the present invention is achieved.

[0016] The following describes some convenient embodiments.

[0017] In some embodiments, the elastic element includes a substantially spherical element. The use of a spherical element reduces the need to orient the elastic element correctly, specifically when the spherical elastic element has substantially isotropic elasticity. The spherical element can be manufactured with good dimensional tolerances. Furthermore, the use of a spherical element allows the elastic element to roll within an annular recess, resulting in minimal (to zero) tangential residual force being exerted on the elastic element, aiding in its axial alignment properties.

[0018] In one embodiment, the dimensions and number of elastic elements are matched to the dimensions of the outer jacket of the first body. While it is preferable to have as many elastic elements as possible, their dimensions should not be too small, as this would increase the tolerances required for all components (the first body, the second body, and the elastic elements). The dimensions of the elastic elements may be in the range of 1% to 10%, preferably 5%, of the radius of the first body. This ratio ensures that approximately 125 elastic elements can be securely fitted into the outer cylindrical jacket of the first body. As an example, the first body may have a total of 120 spherical elastic elements with radii of approximately 100 mm and approximately 4 mm. In this case, the ratio is 4% (=4 / 100).

[0019] In one embodiment, the coil spring is provided with windings that create an elastic element. The coil spring can result in a simpler method of assembling axially aligned assemblies as the number of parts that need to be attached decreases.

[0020] In one embodiment, the elastic element is made of a plastic material such as polyoxymethylene. Alternatively, a rubber element may also be used.

[0021] In one embodiment, the first body has a first contact surface, and the second body has a second contact surface connected to the first contact surface in the connected state of the axial alignment assembly. The first contact surface has a normal that can be oriented substantially parallel to a first alignment axis. The second contact surface has a normal that can be oriented substantially parallel to a second alignment axis. The normals of the first body and the second body are oriented in opposite directions.

[0022] In one embodiment, at least one of the first and second contact surfaces has a surface normal whose component is parallel to the first and / or second alignment axis. The first contact surface may be substantially perpendicular to the outer cylindrical jacket of the first body. The second contact surface may be substantially perpendicular to the inner cylindrical jacket. Thus, at least one of the first and second contact surfaces is positioned perpendicular to the outer and / or inner jacket.

[0023] In one embodiment, the axial alignment assembly includes a holder for holding a plurality of elastic elements. The holder may be provided in a recess formed between the outer cylindrical jacket and the inner cylindrical jacket. The holder enables pre-fabrication of the holder with the plurality of elastic elements, thereby enabling the de facto manufacture of the axial assembly. The holder with the elastic elements may then be inserted between the first body and the second body. Alternatively, the holder may be positioned next to the inner cylindrical jacket of the second body, or the first body may be positioned in a predetermined position.

[0024] In one embodiment, the holder includes a cage for housing the elastic element, specifically in a direction square to the alignment axis.

[0025] In one embodiment, a charged particle microscope is provided that includes an axial alignment assembly as defined herein.

[0026] In one embodiment, the first body is a lens pole piece.

[0027] According to one aspect, a method for axially aligning a first body and a second body is provided, the method comprising: - providing a first body having a substantially cylindrical outer jacket and a first alignment axis; - providing a second body having a substantially cylindrical inner jacket and a second alignment axis; - providing a plurality of elastic elements;

[0028] - positioning the second body relative to the first body such that the inner jacket faces the outer jacket and a substantially annular recess is formed between the inner jacket and the outer jacket; - positioning the plurality of elastic elements in the annular recess such that each elastic element contacts the outer jacket of the first body and the inner jacket of the second body and exerts a force on the outer jacket and the inner jacket to align the first alignment axis and the second alignment axis.

[0029] It can be seen that the methods defined herein can be arranged in various permutations. The above steps do not necessarily have to be performed in the order stated. The positioning of the first body, the second body, and the elastic elements can be: - positioning the first body first, then the second body, and finally the elastic elements; - positioning the first body first, then the elastic elements, and finally the second body; - positioning the second body first, then the first body, and finally the elastic elements; - positioning the second body first, then the elastic elements, and finally the first body; - positioning the elastic elements first, then the first body, and finally the second body; -This may include positioning the elastic element first, then the second body, and finally the first body.

[0030] In one embodiment, the method includes the steps of providing a holder for holding the plurality of elastic elements, and positioning the plurality of elastic elements in the holder. As previously defined, the step of providing the holder can be carried out in several ways. For example, the plurality of elastic elements are positioned in the holder before the combination of the holder and the elastic elements is brought into contact with either the first body or the second body.

[0031] In one embodiment, the plurality of elastic elements are brought into contact with one of the outer jacket and the inner jacket, and then brought into contact with the other of the outer jacket and the inner jacket.

[0032] In one embodiment, the method may include the step of moving the first body relative to the second body in a direction primarily parallel to the first and second alignment axes.

[0033] Herein, the present invention will be described in detail based on exemplary embodiments and accompanying schematic diagrams. [Brief explanation of the drawing]

[0034] [Figure 1] A longitudinal cross-sectional view of a charged particle microscope according to the first embodiment of the present invention is shown. [Figure 2] A longitudinal cross-sectional view of a charged particle microscope according to a second embodiment of the present invention is shown. [Figure 3] This specification shows a longitudinal cross-sectional view passing through the first and second bodies of the axial assembly as defined herein. [Figure 4a] This specification shows a longitudinal cross-sectional view passing through an axial assembly as defined herein. [Figure 4b] Figure 4a shows a close-up view of the axial assembly. [Figure 5] An embodiment of the axial assembly as defined herein is shown. [Figure 6] Specifically, further embodiments of the axial assembly as defined herein, for use in charged particle microscopy, are shown.

[0035] Figure 1 (not to scale) is a very schematic diagram of an embodiment of a charged particle microscope M according to an embodiment of the present invention. More specifically, the figure shows an embodiment of a transmission microscope M, which in this case is a TEM / STEM (although in the context of the present invention, it could be, for example, an SEM (see Figure 2) or an ion-based microscope). In Figure 1, within a vacuum housing 2, an electron source 4 produces an electron beam B that propagates along the electron-optic axis B', crosses an electron-optic emitter 6, and directs / focuses electrons onto a selected portion of a sample S (which may, for example, be (locally) thinned / planarized). A deflector 8 is also shown, which can be used to provide (among other things) a scanning motion of the beam B.

[0036] The sample S is held in a sample holder H, which can be positioned in multiple degrees of freedom by a positioning device / stage A that moves a cradle to which the holder H is (removably) mounted. For example, the sample holder H may have fingers that can move in the XY plane (among many others) (see Cartesian coordinate system in the description; typically, motion parallel to Z and tilting around X / Y are also possible). Such movement allows various parts of the sample S to be illuminated / imaged / inspected by an electron beam B moving along axis B' (in the Z direction) (and / or scanning motion can be performed as an alternative to electron beam scanning). If desired, an optional cooling device (not described) can be brought into close thermal contact with the sample holder H, thereby maintaining the sample holder H (and the sample S on it) at, for example, an extremely low temperature.

[0037] The electron beam B interacts with the sample S in such a way that it causes the sample S to emit various types of "induced" radiation, including (e.g.) secondary electrons, backscattered electrons, X-rays, and photoluminescence (cathodoluminescence). If desired, one or more of these types of radiation can be detected with the help of an analytical device 22, which may be a combination of a scintillator / photomultiplier tube or an EDX or EDS (energy-dispersive X-ray spectroscopy) module, in which case an image can be constructed using essentially the same principles as a SEM. However, alternatively or supplementarily, electrons that traverse (pass through) the sample S, are emitted from the sample S, and continue to propagate along axis B' (substantially, though generally, with some degree of deflection / scattering) can be investigated. Such transmitted electron beams typically enter an imaging system (projection lens) 24 equipped with various electrostatic / magnetic lenses, deflectors, collectors (such as a stigmeter), etc. In standard (non-scattering) TEM mode, the imaging system 24 can collect an electron beam onto a fluorescence screen 26 (as schematically shown by arrow 26') which can be retracted / extended (as schematically shown by arrow 26') to move it out of the path of axis B', if desired. The imaging system 24 then forms a (partial) image (or diffractogram) of the sample S on the screen 26, which can be viewed through a viewing port 28 located in a suitable portion of the wall of the housing 2. The retraction mechanism for the screen 26 can be, for example, virtually mechanical and / or electrical, and is not described here.

[0038] As an alternative to visually inspecting the image on the screen 26, the fact that the electron beam exiting the imaging system 24 has a generally very deep focusing depth (e.g., about 1 meter) can be utilized. As a result, various other types of analytical instruments (such as those listed below) can be used downstream of the screen 26. -TEM camera 30. At the position of camera 30, the electron beam can form a still image (or diffractogram), which can be processed by controller / processor 20 and displayed on a display device 14, such as a flat panel display. When not needed, camera 30 can be retracted / retrieved (as schematically shown by arrow 30') to move the camera off axis B'. -STEM camera 32. The output from camera 32 can be recorded as a function of the (X, Y) scanning position of beam B on sample S, and an image can be constructed which is a "map" of the output from camera 32 as a function of X, Y. Camera 32 may include a single pixel having a diameter of, for example, 20 mm, in contrast to the matrix of pixels characteristic of camera 30. Furthermore, camera 32 is generally different from camera 30 (e.g., 10 2 A much higher acquisition rate (for example, 10 images / second) 6 It has points / second. Again, if not needed, camera 32 can be retracted / extended so as not to obstruct axis B' (such retraction is not considered necessary, for example, in the case of a donut-shaped annular darkfield camera 32, in which case a bundle passage may be possible through the central hole when the camera is not in use) (as schematically shown by arrow 32'). -As an alternative to performing imaging using camera 30 or 32, a spectrometer 34, which can be an EELS module, can also be invoked.

[0039] It should be noted that the order / position of parts 30, 32, and 34 is not strict, and many possible variations are conceivable. For example, the spectrometer 34 can be integrated with the imaging system 24.

[0040] In the illustrated embodiment, the microscope M further comprises a retractable X-ray computed tomography (CT) module, typically indicated by reference no. 40. Computed tomography (also known as tomographic imaging) uses an electron source and (diametrically opposed) detectors to examine a sample along various lines of sight to obtain insightful observations of the sample from various viewpoints.

[0041] Note that the controller (computer processor) 20 is connected to the various components shown in the diagram via control lines (buses) 20'. This controller 20 can provide various functions such as synchronizing actions, providing setpoints, processing signals, performing calculations, and displaying messages / information on a display device (not shown). Needless to say, the controller 20 (diagrammatically depicted) may be inside or outside the enclosure 2 as desired, and may be a single integrated unit or a composite unit.

[0042] Those skilled in the art will understand that the interior of the housing 2 does not need to be kept in a strict vacuum. For example, in so-called "environmental TEM / STEM," a given gaseous background atmosphere is intentionally introduced / maintained within the housing 2. Those skilled in the art will also understand that, in practice, it may be advantageous to limit the volume of the housing 2 so as to essentially enclose axis B' by taking the form of a small tube (e.g., about 1 cm in size) that extends outward to accommodate structures such as the electron source 4, sample holder H, screen 26, camera 30, camera 32, and spectrometer 34, through which the employed electron beam passes.

[0043] Referring now to Figure 2, another embodiment of the apparatus according to the present invention is shown. Figure 2 (not to scale) is a very schematic depiction of a charged particle microscope M according to the present invention, more specifically, an embodiment of a non-transmission microscope M, in this case a SEM (although in the context of the present invention, an ion-based microscope, for example, may also be equally valid). In the figure, components corresponding to items in Figure 1 are indicated using the same reference numerals and are not described separately here. The following components (among others) are added to those in Figure 1: -2a: Vacuum port, which can be opened to take items (components, samples) into / out of the vacuum chamber 2, or in addition, auxiliary devices / modules can be attached, for example. Microscope M may be provided with multiple such ports 2a if desired. -10a, 10b: Schematic depiction of the lens / optical element in the light-emitting body 6. -12: A voltage source, if necessary, that allows the sample holder H or at least the sample S to be biased (float) to a certain potential relative to ground. -14: A display such as an FPD or CRT. -22a, 22b: (A segmented electron detector 22a comprises multiple independent detection segments (e.g., quadrants) arranged around a central aperture 22b (allowing the passage of beam B). Such a detector may be used, for example, to investigate the angular dependence of the output (secondary or backscattered) electron bundle coming out of a sample S.

[0044] Several components of the charged particle microscope shown in Figures 1 and 2 need to be aligned axially. However, it is often required that two or more components be aligned axially. For this reason, this disclosure provides an axial alignment assembly.

[0045] Now, moving to Figure 3, an assembly 100 is shown comprising a first substantially cylindrical body 101 having a first axial alignment axis A1 and a second substantially cylindrical body 201 having a second axial alignment axis A2. It can be seen that the first body 101 and the second body 201 do not necessarily have to be cylindrical. As defined herein, the first body 101 comprises a substantially cylindrical outer jacket 103 and has a first alignment axis A1. In light of this disclosure, a substantially solid first body is also conceivable, but the first body 101 may have a central bore 104 as shown in Figure 3. The second body 201 as defined herein comprises a substantially cylindrical inner jacket 203 and has a second alignment axis A2. In the illustrated embodiment, the second body 201 has an annular projection 202 extending toward the second alignment axis A2. Referring to Figure 4b in more detail, the annular projection 202 allows the first body 101 to sit on the projection of the second body 201. Further referring to Figure 3, it can be seen that the second body 201 is positioned relative to the first body 101 such that the inner jacket 203 faces the outer jacket 103. A substantially annular recess 401 is formed between the inner jacket 103 and the outer jacket 203. In Figure 3, it can be seen that the first axis A1 is not properly aligned with the second axis A2. The dimensions of the annular recess are smaller on the right side of Figure 3 and slightly wider on the left side. The alignment of these two bodies presents a challenge.

[0046] Now, moving to Figure 4a, it can be seen that the first body 101 and the second body 201 can be aligned with their alignment axes A1 and A2 by providing a plurality of elastic elements 301 and 302 positioned within the annular recess 401. Each of the plurality of elastic elements 301 and 302 is in contact with the outer jacket 103 of the first body 101 and the inner jacket 203 of the second body 201. The elastic elements 301 and 302, as well as the first body 101 and the second body 201, are shaped such that each of the elastic elements 301 and 302 exerts a force on the outer jacket 103 and the inner jacket 203, respectively, in order to align the first alignment axis A1 and the second alignment axis A2.

[0047] In the incorrectly aligned state shown in Figure 3, the annular recess 401 appears smaller on the right side of the figure and larger on the left side. By providing multiple elastic elements 301, 302 within the annular recess 401, each having substantially the same nominal dimensions, the elastic elements 302 located in the narrower part of the recess 401 are compressed more significantly than the elastic elements 301 located in the wider part of the recess 401. This greater compression causes the elastic elements 302 in the narrower part of the recess 401 to exert greater force on the cylindrical jackets 103, 203 than the elastic elements 301 in the wider part of the recess 401. The resulting force pushes the first body 101 away from the second body 201 in the direction of the wider part. This causes the narrower part of the recess to widen and the wider part to narrow. This balance of forces continues until the alignment axis A1 of the first body 101 is substantially aligned with the alignment axis A2 of the second body 201, and the alignment axes coincide and become a single aligned axis A (as shown in Figure 4a).

[0048] Figure 4b shows details of the axial alignment assembly 100 as shown in Figure 4a. Here, it can be seen that the first body 101 has a first contact surface 105 and the second body 201 has a second contact surface 205. The first contact surface 105 and the second contact surface 205 are mainly parallel to each other. The first contact surface 105 and the second contact surface 205 are mainly orthogonal to the corresponding inner / outer jackets 103, 203 of the first and second bodies 101, 201. In Figure 4b, it can be seen that the axial alignment assembly as defined herein does not require axial compressive forces to be applied to the first body 101 and the second body 201. The axial alignment force is established by the dimensioning of the outer jacket 103, the inner jacket 203 and the elastic element 301.

[0049] In this specification, the axial alignment assembly 100 as defined is described in relation to a cylindrical body and an annular recess. It is also possible that other degrees of rotational symmetry may be applied to the axial alignment assembly as defined herein, instead of a cylindrical body. For example, triangular, quadrilateral, polygonal, and other shapes are within the scope of this disclosure and are considered equivalent to the cylindrical body described above. In these examples, spherical elastic elements may be used. The applicant reserves the right to file one or more divisional applications concerning these points.

[0050] It is further evident that the embodiment discloses the use of spherical elastic elements. These are advantageous because the elements do not need to be aligned in a particular way in order to function properly. However, other shapes are also possible.

[0051] Figure 4b shows that the contact surfaces 105 and 205 can be brought into direct contact. Alternatively, a seal element (not shown) may be provided between the first body 101 and the second body 201 such that the contact surface 105 of the first body 101 contacts a first side surface of the seal element, and the contact surface 205 of the second body 201 contacts the other second side surface of the seal element. The seal element may be relatively thin and can ensure a pressure seal between the inner portion of the assembly (located near the central axis A) and the radially outer portion of the first body. In some embodiments, the seal element may be made of rubber. In other embodiments, the seal element may be made of metal. This is advantageous when it is desired that the inner portion of the axial alignment assembly (i.e., the space located near the central axis A) has a very low pressure, such as (almost) a vacuum. This allows the metal seal element to provide a vacuum seal to the axial alignment assembly as defined herein. This is advantageous when used in charged particle microscopes, as will be described below.

[0052] Figure 5 shows an alternative embodiment of the axial alignment assembly 100. It can be seen that the corresponding elements are identified using the corresponding reference numerals. The main difference from the axial alignment assembly shown in Figure 4a is the use of a holder 311 for holding the elastic elements 301, 302 in place. The holder 311 is prepared before the assembly of the two bodies 101, 201 by adding the elastic elements 301, 302 to the holder 311. The holder 311 can be a cargo for holding the spherical elastic elements 301, 302. Other embodiments of the holder 311 are also possible.

[0053] Figure 6 shows some embodiments of a charged particle microscope in which a total of three bodies 1101, 1102, and 201 are aligned using the assembly defined herein. Here, the most important alignment is considered to be the alignment of the upper body 1101 and the lower body 1102. In the embodiment shown in Figure 6, the upper body 1101 and the lower body 1102 are the upper and lower pole pieces 1102, respectively, of the lens for a charged particle microscope, such as the charged particle microscope shown in Figure 1 or Figure 2. The axial alignment assembly 100 defined herein provides an excellent method for aligning the upper objective pole 1101 and the lower objective pole 1102 of a TEM.

[0054] The required alignment between the upper and lower objective magnetic poles is approximately 1 μm in size and can be achieved with an axial assembly as shown in Figure 6. Here, the upper body 1101 is axially aligned with respect to the outer body 201 by using a spherical elastic element 301 in the upper annular recess, and the lower body 1102 is axially aligned with respect to the outer body 201 by using a spherical elastic element 401 in the lower annular recess. This also results in the upper body 1101 being axially aligned with respect to the lower body 1102. The elastic elements 301 and 401 can be provided in their respective holders 311 and 411, such as cages as shown in Figure 6.

[0055] In measurements of axially aligned assemblies as defined herein, concentricity of a few microns can be obtained relatively easily.

[0056] As previously stated, an axial alignment assembly as defined herein can be used to provide an ultra-high vacuum (UHV) sample chamber. It is generally accepted that achieving UHV requires the feasibility of metal sealing and firing. In axial alignment assemblies known from the prior art, two bodies are required to exert forces on each other to achieve axial alignment. The use of metal seals is thought to significantly increase the axial compressive force required to obtain the desired axial alignment. In contrast, the axial alignment assembly as defined herein does not require the use of axial force to obtain axial alignment, thereby allowing the use of metal seals. For example, in the case of a ball array in a cylindrical gap, using the axial alignment assembly as defined herein does not hinder the compression of the metal seal between, for example, the pole pieces 1101, 1102 and the "inner objective block" 201. In this case, a UHV sample chamber can be obtained in a charged particle microscope.

[0057] Embodiments of the present invention have been described above. The desired protection is defined by the appended claims.

Claims

1. An axial alignment assembly (100) comprising: a first body (101) with a substantially cylindrical outer jacket (103) and having a first alignment axis (A1); a second body (201) with a substantially cylindrical inner jacket (203) and having a second alignment axis (A2), the second body (201) being positioned relative to the first body (101) such that the inner jacket (203) faces the outer jacket (103) and a substantially annular annular recess (401) is formed between the inner jacket and the outer jacket; an axial alignment assembly (100) comprising: a plurality of elastic elements (301, 302) positioned within the annular recess (401), each elastic element (301, 302) contacting the outer jacket (103) of the first body (101) and the inner jacket (203) of the second body (201) and exerting a force on the outer jacket (103) and the inner jacket (203) to align the first alignment axis (A1) and the second alignment axis (A2).

2. 2. The axial alignment assembly (100) of claim 1, wherein the elastic elements (301, 302) have nominal dimensions that exceed a nominal distance between the outer jacket (103) and the inner jacket (203).

3. 3. The axial alignment assembly (100) of claim 1 or 2, wherein the elastic elements (301, 302) comprise substantially spherical elements (301, 302).

4. The axial alignment assembly (100) according to any one of claims 1 to 3, wherein the elastic elements (301, 302) are made of a plastic material.

5. 5. The axial alignment assembly (100) of claim 1, wherein the first body has a first abutment surface (105) and the second body has a second abutment surface (205) connected to the first abutment surface.

6. 6. The axial alignment assembly (100) of claim 5, wherein at least one of the first abutment surface (105) and the second abutment surface (205) has a surface normal that has a component parallel to the first alignment axis (A1) and / or the second alignment axis (A2).

7. 7. The axial alignment assembly (100) of claim 5 or 6, wherein at least one of the first abutment surface (105) and the second abutment surface (205) is positioned orthogonal to the outer jacket (103) and / or the inner jacket (203).

8. 8. The axial alignment assembly (100) of any one of claims 1 to 7, wherein the axial alignment assembly (100) comprises a holder (311) for holding the plurality of elastic elements (301, 302).

9. 9. The axial alignment assembly (100) according to claim 8, wherein the holder (311) comprises a cage for accommodating the elastic elements (301, 302), particularly in a direction parallel to the alignment axis (A, A1, A2).

10. A charged particle microscope comprising an axial alignment assembly (100) according to any one of claims 1 to 9.

11. 11. The charged particle microscope of claim 10, wherein the first body is a magnetic pole piece (1101, 1102).

12. 1. A method of axially aligning a first body and a second body, comprising: - providing a first body (101) with a substantially cylindrical outer jacket (103) and having a first alignment axis (A1); - providing a second body (201) with a substantially cylindrical inner jacket (203) and having a second alignment axis (A2); - providing a plurality of elastic elements (301, 302), - positioning the second body (201) relative to the first body (201) so that the inner jacket (203) faces the outer jacket (103) and a substantially annular recess (401) is formed between the inner jacket (203) and the outer jacket (103); - positioning the plurality of elastic elements (301, 302) in the annular recess (401) such that each elastic element (301, 302) contacts the outer jacket (103) of the first body (101) and the inner jacket (203) of the second body (201) and exerts a force on the outer jacket (103) and on the inner jacket (203) to align the first alignment axis (A1) and the second alignment axis (A2).

13. 13. The method of claim 12, further comprising the steps of: providing a holder (311) for holding the plurality of elastic elements (301, 302); and positioning the plurality of elastic elements (301, 302) in the holder (311).

14. 14. The method according to claim 12 or 13, wherein the plurality of elastic elements (301, 302) are first brought into contact with one of the outer jacket (103) and the inner jacket (203) and then brought into contact with another of the outer jacket (103) and the inner jacket (203).

15. 15. The method of claim 14, comprising moving the first body (101) relative to the second body (201) in a direction primarily parallel to the first alignment axis (A1) and the second alignment axis (A2).

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